This is an investigation of the structural antecedents and behavioral consequences of interpersonal networks. The basic question of this study is whether ethnicity has any persisting relevance. And further, if it does, is it due to the retention of cultural heritage or the operation of the American social structure and the position of individuals in the social structure. Historical-ecological research we are now completing indicates that the emergence and persistence of communities depends upon (1) the macroscopic structure of the city--in particular the urban industrial structure, (2) the character of residential communities and (3) the position of individuals and groups in the urban occupational structure. This proposal is a request for funds for (1) completion of the analysis of 1,781 interviews representative of the Philadelphia Urbanized Area, (2) an investigation of the migration of ethnic groups in the United States in 1900, (3) an investigation of the relationship between work and residence in 1936, (4) an investigation of the employment structure of the Philadelphia metropolitan area in 1970, and (5) a pilot study of the information contained in the immigrant ships' passenger lists.